Structural Adhesives

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A structural adhesive can be described as a high-strength adhesive material that is isotropic in nature and bonds two or more parts together in a load-bearing structure. A structural adhesive material must be capable of transmitting the stress/load without loss of structural integrity within design limits. There are many types of established structural adhesives, including epoxy, urethane, acrylic, silicone, etc.

Structural Adhesivescomprises nine chapters and is divided into two parts: Part 1, Preparation, Properties, and Characterization; Part 2, Applications.

The topics covered include: structural epoxy adhesives; biological reinforcement of epoxies as structural adhesives; marble dust reinforced epoxy structural adhesive composites; characterization of various structural adhesive materials; effects of shear and peel stress distributions on the behavior of structural adhesives; the inelastic response of structural aerospace adhesives; structural reactive acrylic adhesives: their preparation, characterization, properties, and applications; application of structural adhesives in composite connections; and naval applications of structural adhesives.

Audience

This book should be of much use and interest to adhesionists, materials scientists, adhesive technologists, polymer scientists, and those working in the construction, railway, automotive, aviation, bridge, and shipbuilding industries.

Kashmiri Lal Mittalwas employed by the IBM Corporation from 1972 through 1993. Currently, he is teaching and consulting worldwide in the broad areas of adhesion as well as surface cleaning. He has received numerous awards and honors including the title of doctorhonoris causafrom Maria Curie-Sklodowska University, Lublin, Poland. He is the editor of more than 160 books dealing with adhesion measurement, adhesion of polymeric coatings, polymer surfaces, adhesive joints, adhesion promoters, thin films, polyimides, surface modification surface cleaning, and surfactants.

S. K. Panigrahi, PhD,is a professor in the Department of Mechanical Engineering of the Defence Institute of Advanced Technology (DIAT), Pune, India. He has worked as an international visiting academic with the University of New South Wales at the Australian Defence Force Academy. With over 27 years of extensive teaching, research, training, and administrative experience, Dr. Panigrahi is currently focused on advanced finite element methods, nonlinear finite element analyses, and modeling engineering structures with functionally graded/monolithic adhesively-bonded joints. His publications include over 190 research articles and peer-reviewed scholarly papers, four books, a monograph, and many conference proceedings, including a series of lecture materials.

Preface xiii

Part 1: Preparation, Properties and Characterization 1

1 Structural Epoxy Adhesives 3
Chunfu Chen

1.1 Introduction 4

1.2 Epoxy Adhesive Chemistry 4

1.2.1 Epoxy Resins 4

1.2.2 Curing Agents and Catalysts 7

1.2.3 Formulating Epoxy Adhesives 10

1.3 Properties, Testing and Characterization 11

1.4 Typical Epoxy Adhesives 13

1.4.1 Room Temperature Cure Epoxy Adhesives 13

1.4.2 Thermal Cure Epoxy Adhesives 14

1.4.3 UV Cure Epoxy Adhesives 16

1.5 Recent Developments and New Trends 18

1.5.1 High Performance Toughened Epoxy Adhesives 18

1.5.2 Low Temperature Cure One-Component Epoxy Adhesives 19

1.5.3 Instant Bonding Epoxy Adhesives 20

1.5.4 Sustainable Epoxy Adhesive Development 22

1.6 Summary 22

References 23

2 Biological Reinforcement of Epoxies as Structural Adhesives 31
Anna Rudawska, Jakub Szabelski, Izabela Miturska-Baraska and Elbieta Doluk

2.1 Introduction 31

2.2 Epoxy Resins and Curing Agents 33

2.2.1 Epoxy Resins 33

2.2.2 Curing Agents 34

2.2.3 Curing Methods 38

2.2.4 Epoxy Structural Adhesives 40

2.3 Modification of Epoxies, and Modifying Agents 41

2.3.1 Epoxy Modification Methods 41

2.3.2 Fillers Properties 44

2.3.3 Fillers Types 45

2.3.3.1 Filler Classification Criterion: Type of Material 46

2.3.3.2 Filler Classification Criterion: Shape of the Filler Particles 47

2.3.3.3 Filler Classification Criterion: Filler Particle Size 48

2.3.3.4 Filler Classification Criterion: Origin 49

2.3.3.5 Filler Classification Criterion: Activity 50

2.4 Biological Reinforcement of Epoxy Adhesives 51

2.4.1 Introduction 51

2.4.2 Types of Biological Reinforcements 51

2.4.2.1 Natural Fibers 53

2.4.2.2 Wood 53

2.4.2.3 Vegetable Oils 58

2.4.2.4 Fungi 59

2.4.2.5 Extracted Plant Ingredients 60

2.4.2.6 Nut Shells 64

2.4.2.7 Straw 65

2.4.3 Natural Fibers 66

2.4.4 Plant Fibers 68

2.4.4.1 Cotton Fibers 68

2.4.4.2 Hemp Fibers 68

2.4.4.3 Linen (Flax) Fibers 69

2.4.4.4 Jute Fibers 71

2.4.4.5 Sisal Fibers 72

2.4.4.6 Coconut (Coir) Fibers 73

2.4.4.7 Cellulose Fibers 74

2.4.4.8 Bamboo Fibers 76

2.4.4.9 Kenaf Fibers 77

2.4.4.10 Other Fibers 78

2.5 Fungi-Modified Adhesives 80

2.6 Prospects 83

2.7 Summary 84

References 85

3 Marble Dust Reinforced Epoxy Structural Adhesive Composites 105
Amar Patnaik, Pankaj Agarwal, Ankush Sharma, Deepika Shekhawat and Tapan Kumar Patnaik

3.1 Introduction 106

3.2 Materials and Methods 110

3.2.1 Procurement of Raw Materials 110

3.2.2 Fabrication of Composites 111

3.2.3 Physical and Mechanical Characterization 113

3.2.3.1 Density and Void Content 113

3.2.3.2 Water Absorption 114

3.2.3.3 Vickers Hardness 115

3.2.3.4 Tensile Test 115

3.2.3.5 Flexure Test 117

3.2.3.6 Impact Test 117

3.2.3.7 Thermal Conductivity 117

3.2.3.8 Specific Wear Rate 117

3.2.3.9 TOPSIS Approach 118

3.3 Results and Discussion 119

3.3.1 Density and Void Content 119

3.3.2 Water Absorption 120

3.3.3 Hardness 121

3.3.4 Tensile Strength and Tensile Modulus 121

3.3.5 Flexural Strength and Flexural Modulus 122

3.3.6 Impact Energy 123

3.3.7 Thermal Conductivity 123

3.3.8 Specific Wear Rate 125

3.3.9 Ranking of Epoxy Adhesive Composites 126

3.4 Summary and Conclusions 131

References 132

4 Characterization of Various Structural Adhesive Materials 135
Srujan Sapkal, Pooja Maske, S. K. Panigrahi and Himanshu S. Panda

List of Abbreviations 136

List of Symbols 137

4.1 Introduction 138

4.2 Various Structural Adhesives and their Properties 139

4.2.1 Phenolic Structural Adhesives 139

4.2.2 Epoxy Structural Adhesives 140

4.2.3 Polyurethane (PU) Structural Adhesives 141

4.2.4 Acrylic Structural Adhesives 142

4.2.5 Cyanoacrylate Structural Adhesives 143

4.2.6 Silicone Structural Adhesives 143

4.3 Characterization Techniques for Structural Adhesives 144

4.3.1 Chemical Characterization 144

4.3.1.1 Energy Dispersive X-ray (EDX) 144

4.3.1.2 X-ray Photoelectron Spectroscopy (XPS) 145

4.3.1.3 Fourier Transform Infrared Spectroscopy (FTIR) 147

4.3.1.4 Gas-Liquid Chromatography (GLC) 151

4.3.1.5 Nuclear Magnetic Resonance 153

4.3.1.6 Raman Spectroscopy 156

4.3.2 Physical Characterization 161

4.3.2.1 Contact Angle Measurement 161

4.3.2.2 Scanning Electron Microscopy (SEM) 164

4.3.2.3 Gelation Time 165

4.3.2.4 Small Angle X-ray Scattering (SAXS) 166

4.3.2.5 Atomic Force Microscopy (AFM) 167

4.3.3 Thermal Characterization 168

4.3.3.1 Thermogravimetric Analysis (TGA) 170

4.3.3.2 Differential Thermal Analysis (DTA) 171

4.3.3.3 Differential Scanning Calorimetry (DSC) 172

4.3.4 Mechanical Characterization 176

4.3.4.1 Tensile Test 177

4.3.4.2 Lap Shear Test 178

4.3.4.3 Dynamic Mechanical Analysis (DMA) 179

4.4 Summary 185

Acknowledgements 186

References 186

5 The Effects of Shear and Peel Stress Distributions on the Behavior of Structural Adhesives in TubularComposite Joints 193
Mohammad Shishesaz

5.1 Introduction 194

5.1.1 A Brief Review of Loads (Stresses) and Failure of Adhesively Bonded Tubular Composite Joints 194

5.1.2 Major Factors Affecting the Peel and Shear Stresses in the Adhesive Layer and its Performance (Failure) 199

5.2 Governing Equations Based on Linear Elasticity 200

5.2.1 Typical Assumptions in a Tubular Lap Joint under Torsion 200

5.3 Factors Influencing the Adhesive Behavior and Stresses 209

5.3.1 The Effects of Geometric and Mechanical Properties of the Adhesive and Adherends 209

5.3.2 The Effects of Load Type on the Adhesive Stresses and Behavior 217

5.3.3 The Effects of Damages due to Voids, Debonds, or Delaminations 221

5.3.4 Additional Factors Influencing the Adhesive Behavior and Its Performance 230

5.3.5 The Effect of Nonlinear Behavior of the Adhesive on Its Performance 236

5.3.6 Factors Influencing the Failure Behavior of the Adhesive Layer 238

5.4 Design Aspects Regarding the Selection of Adhesive Layer 239

5.5 Summary 244

Acknowledgement 245

Nomenclature 245

References 249

6 Inelastic Response of Structural Aerospace Adhesives 255
Yi Chen and Lloyd Smith

List of Symbols 255

6.1 Introduction 257

6.2 Time-Independent Plasticity 258

6.2.1 Yield Stress 258

6.2.2 Elasto-Plastic Models 262

6.3 Time-Dependent Inelasticity 263

6.3.1 Creep Loading 263

6.3.2 Cyclic Loading 267

6.3.3 Time-Dependent Models 270

6.3.3.1 Modeling of Creep 270

6.3.3.2 Modeling of Ratcheting 274

6.4 Environmental Factors 276

6.4.1 Temperature 276

6.4.2 Moisture 277

6.4.3 Modeling 278

6.5 Summary 280

References 281

Part 2: Applications 291

7 Structural Reactive Acrylic Adhesives: Preparation, Characterization, Properties and Applications 293
D.A. Aronovich and L.B. Boinovich

7.1 Introduction 293

7.2 ompositions and Chemistries 295

7.2.1 Base Monomer 296

7.2.2 Thickeners and Elastomeric Components 299

7.2.3 Adhesive Additives 308

7.2.4 Initiators 310

7.2.5 Aerobically Curable Systems 319

7.2.6 Fillers 319

7.3 Physico-Mechanical Properties of SAAs 323

7.4 Adhesives for Low Surface Energy Materials 329

7.4.1 Initiators Based on Trialkylboranes 329

7.4.2 Comparison of the Initiation System Containing Trialkylborane with the Redox System Benzoyl Peroxide (BPO) - Tertiary Aromatic Amine 340

7.4.3 Alternative Types of Trialkylborane Initiators 342

7.4.4 Additives Modifying the Curing Stage 344

7.4.5 Other Components of SAAs 346

7.4.6 Hybrid SAAs 348

7.5 Comparison of the Properties of SAAs and Other Reactive Adhesives 354

7.6 Summary and Outlook 358

References 359

8 Application of Structural Adhesives in Composite Connections 375
M. D. Banea and H.F.M. de Queiroz

8.1 Introduction 375

8.2 Factors Affecting the Performance of Composite Adhesive Joints 376

8.2.1 Effect of Surface Preparation 377

8.2.2 Effect of Joint Configuration and Failure Mode 378

8.2.3 Effect of Mechanical Properties of Adhesive and Adherend Materials 383

8.2.4 Effect of the Environmental Conditions 386

8.3 Recent Developments and Trends 388

8.4 Summary 389

References 390

9 Naval Applications of Structural Adhesives 397
Bikash Chandra Chakraborty

List of Abbreviations 398

List of Symbols with Units 399

9.1 Introduction 400

9.2 Type of Marine Adhesives 401

9.2.1 Essential Characteristics 402

9.2.2 Flexible Adhesives 403

9.2.2.1 Bonding Multilayer Rubber Tiles 406

9.2.2.2 Bonding Silicone Rubber Gaskets 407

9.2.3 Thermoset-Based Marine Adhesives 408

9.3 Application on Naval Platform 415

9.3.1 Vibrodamping Arrangements 415

9.3.2 Underwater Application 416

9.3.3 Acid-Resistant Rubber Bonding 421

9.3.3.1 Example 422

9.4 Diffusion of Water in Adhesive Matrix 423

9.4.1 Fickian Diffusion 423

9.4.1.1 Example 427

9.4.2 Dual-Fickian Prediction 430

9.4.3 Effect on Flexural Strength 431

9.4.3.1 Example 432

9.5 Summary 436

References 437

Index 445